In the mammalian central nervous system (CNS), the transmission of nerve impulses is controlled by the interaction between a neurotransmitter, that is released by a sending neuron, and a surface receptor on a receiving neuron, which causes excitation of this receiving neuron. L-Glutamate, which is the most abundant neurotransmitter in the CNS, mediates the major excitatory pathway in mammals, and is referred to as an excitatory amino acid (EAA). The receptors that respond to glutamate are called excitatory amino acid receptors (EM receptors). See Watkins and Evans, Ann. Rev. Pharmacol. Toxicol., 21, 165 (1981); Monaghan, Bridges, and Cotman, Ann. Rev. Pharmacol. Toxicol., 29, 365 (1989); Watkins, Krogsgaard-Larsen, and Honore, Trans. Pharm. Sci., 11, 25 (1990). The excitatory amino acids are of great physiological importance, playing a role in a variety of physiological processes, such as long-term is potentiation (leaming and memory), the development of synaptic plasticity, motor control, respiration, cardiovascular regulation, and sensory perception.
Excitatory amino acid receptors are classified into two general types. Receptors that are directly coupled to the opening of cation channels in the cell membrane of the neurons are termed xe2x80x9cionotropicxe2x80x9d. This type of receptor has been subdivided into at least three subtypes, which are defined by the depolarizing actions of the selective agonists N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole4-propionic acid (AMPA), and kainic acid (KA). The second general type of receptor is the G-protein or second messenger-linked xe2x80x9cmetabotropicxe2x80x9d excitatory amino acid receptor. This second type is coupled to multiple second messenger systems that lead to enhanced phosphoinositide hydrolysis, activation of phospholipase D, increases or decreases in c-AMP formation, and changes in ion channel function. Schoepp and Conn, Trends in PharmacoL Sci., 14, 13 (1993). Both types of receptors appear not only to mediate normal synaptic transmission along excitatory pathways, but also participate in the modification of synaptic connections during development and throughout life. Schoepp, Bockaert, and Sladeczek, Trends in Phannacol. Sci., 11, 508 (1990); McDonald and Johnson, Brain Research Reviews, 15, 41 (1990).
AMPA receptors are assembled from four protein sub-units known as GluR1 to GluR4, while kainic acid receptors are assembled from the sub-units GluR5 to GluR7, and KA-1 and KA-2. Wong and Mayer, Molecular Pharmacology 44: 505-510, 1993. It is not yet known how these sub-units are combined in the natural state. However, the structures of certain human variants of each sub-unit have been elucidated, and cell lines expressing individual sub-unit variants have been cloned and incorporated into test systems designed to identify compounds which bind to or interact with them, and hence which may modulate their function. Thus, European patent application, publication number EP-A2-0574257 discloses the human sub-unit variants GluR1B, GluR2B, GluR3A and GluR3B. European patent application, publication number EP-A1-0583917 discloses the human sub-unit variant GluR4B.
One distinctive property of AMPA and kainic acid receptors is their rapid deactivation and desensitization to glutamate. Yamada and Tang, The Joumal of Neuroscience, September 1993, 13(9): 3904-3915 and Kathryn M. Partin, J. Neuroscience, Nov. 1, 1996, 16(21): 6634-6647.
It is known that the rapid desensitization and deactivation of AMPA and/or kainic acid receptors to glutamate may be inhibited using certain compounds. This action of these compounds is often referred to in the alternative as xe2x80x9cpotentiationxe2x80x9d of the receptors. One such compound, which selectively potentiates AMPA receptor function, is cyclothiazide. Partin et al., Neuron. Vol. 11, 1069-1082, 1993.
International Patent Application Publication WO 98/33496 published Aug. 6, 1998 discloses certain sulfonamide derivatives which are useful, for example, for treating psychiatric and neurological disorders, for example cognitive disorders; neuro-degenerative disorders such as Alzheimer""s disease; age-related dementias; age-induced memory impairment; movement disorders such as tardive dyskinesia, Huntington""s chorea, myoclonus, and Parkinson""s disease; reversal of drug-induced states (such as cocaine, amphetamines, alcohol-induced states); depression; attention deficit disorder; attention deficit hyperactivity disorder; psychosis; cognitive deficits associated with psychosis, and drug-induced psychosis.
The present invention provides compounds of formula 1: 
or a pharmaceutically acceptable salt thereof.
The present invention further provides a compound of formula Ia: 
or a pharmaceutically acceptable salt thereof.
The present invention further provides a method of potentiating glutamate receptor function in a patient which comprises administering to said patient an effective amount of a compound of formula Ha.
In addition, the present invention provides a method of treating depression in a patient comprising administering to said patient an effective amount of a compound of formula Ia.
The present invention further provides a method of treating schizophrenia in a patient comprising administering to said patient an effective amount of a compound of formula Ia.
Furthermore, the present invention provides a method of treating cognitive disorders in a patient comprising administering to said patient an effective amount of a compound of formula Ia.
The invention further provides pharmaceutical compositions of compounds of formula Ia, including the hydrates thereof, comprising, as an active ingredient, a compound of formula Ia in combination with a pharmaceutically acceptable carrier, diluent or excipient.
This invention also encompasses novel intermediates, and processes for the synthesis of the compounds of formula Ia.
In addition, the present invention provides the use of a compound of formula Ia or a pharmaceutically acceptable salt thereof for potentiating glutamate receptor function.
According to another aspect, the present invention provides the use of a compound of formula Ia for the manufacture of a medicament for potentiating glutamate receptor function.
The present invention further provides an article of manufacture comprising packaging material and a compound of formula Ia or a pharmaceutically acceptable salt thereof contained within said packaging material, wherein said packaging material comprises a label which indicates that said compound of formula Ia can be used for treating at least one of the following; Alzheimer""s disease, schizophrenia, cognitive deficits associated with schizophrenia, depression, and cognitive disorders.
In this specification, the term xe2x80x9cpotentiating glutamate receptor functionxe2x80x9d refers to any increased responsiveness of glutamate receptors, for example AMPA receptors, to glutamate or an agonist, and includes but is not limited to inhibition of rapid desensitization or deactivation of AMPA receptors to glutamate.
A wide variety of conditions may be treated or prevented by the compounds of formula I and their pharmaceutically acceptable salts through their action as potentiators of glutamate receptor function. Such conditions include those associated with glutamate hypofunction, such as psychiatric and neurological disorders, for example cognitive disorders; neuro-degenerative disorders such as Alzheimer""s disease; age-related dementias; age-induced memory impairment; movement disorders such as tardive dyskinesia, Huntington""s chorea, myoclonus, dystonia, and Parkinson""s disease; reversal of drug-induced states (such as cocaine, amphetamines, alcohol-induced states); depression; attention deficit disorder; attention deficit hyperactivity disorder; psychosis; cognitive deficits associated with psychosis, and drug-induced psychosis. In addition, the compounds of formula I are useful for treating sexual dysfunction. The compounds of formula I may also be useful for improving memory (both short term and long term) and learning ability. The present invention provides the use of compounds of formula I for the treatment of each of these conditions.
It is understood by one of ordinary skill in the art that the compound of formula Ia: 
is included within the scope of formula I defined hereinabove. More specifically, formula I is a racemic mixture and formula Ia is the corresponding (R)-enantiomer.
The present invention includes the pharmaceutically acceptable salts of the compounds defined by formula I and formula Ia. The term xe2x80x9cpharmaceutically acceptable saltxe2x80x9d as used herein, refers to salts of the compounds of the above formula which are substantially non-toxic to living organisms. Typical pharmaceutically acceptable salts include those salts prepared by reaction of the compounds of the present invention with a pharmaceutically acceptable organic or inorganic base. Such salts are known as base addition salts. Such salts include the pharmaceutically acceptable salts listed in Journal of Pharmaceutical Science, 66, 2-19 (1977) which are known to the skilled artisan.
Base addition salts include those derived from inorganic bases, such as ammonium or alkali or alkaline earth metal hydroxides, carbonates, bicarbonates, and the like. Such bases useful in preparing the salts of this invention thus include sodium hydroxide, potassium hydroxide, ammonium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, calcium hydroxide, calcium carbonate, and the like. The potassium and sodium salt forms are particularly preferred.
It should be recognized that the particular counterion forming a part of any salt of this invention is usually not of a critical nature, so long as the salt as a whole is pharmacologically acceptable and as long as the counterion does not contribute undesired qualities to the salt as a whole. It is further understood that the above salts may form hydrates or exist in a substantially anhydrous form.
As used herein, the term xe2x80x9cstereoisomerxe2x80x9d refers to a compound made up of the same atoms bonded by the same bonds but having different three-dimensional structures which are not interchangeable. The three-dimensional structures are called configurations. As used herein, the term xe2x80x9cenantiomerxe2x80x9d refers to two stereoisomers whose molecules are nonsuperimposable mirror images of one another. The term xe2x80x9cchiral centerxe2x80x9d refers to a carbon atom to which four different groups are attached. As used herein, the term xe2x80x9cdiastereomersxe2x80x9d referes to stereoisomers which are not enantiomers. In addition, two diastereomers which have a different configuration at only one chiral center are referred to herein as xe2x80x9cepimersxe2x80x9d. The terms xe2x80x9cracematexe2x80x9d, xe2x80x9cracemic mixturexe2x80x9d or xe2x80x9cracemic modificationxe2x80x9d refer to a mixture of equal parts of enantiomers.
The term xe2x80x9cenantiomeric enrichmentxe2x80x9d as used herein refers to the increase in the amount of one enantiomer as compared to the other. A convenient method of expressing the enantiomeric enrichment achieved is the concept of enantiomeric excess, or xe2x80x9ceexe2x80x9d, which is found using the following equation:   ee  =                              E          1                -                  E          2                                      E          1                +                  E          2                      xc3x97    100  
wherein E1 is the amount of the first enantiomer and E2 is the amount of the second enantiomer. Thus, if the initial ratio of the two enantiomers is 50:50, such as is present in a racemic mixture, and an enantiomeric enrichment sufficient to produce a final ratio of 70:30 is achieved, the ee with respect to the first enantiomer is 40%. However, if the final ratio is 90:10, the ee with respect to the first enantiomer is 80%. An ee of greater than 90% is preferred, an ee of greater than 95% is most preferred and an ee of greater than 99% is most especially preferred. Enantiomeric enrichment is readily determined by one of ordinary skill in the art using standard techniques and procedures, such as gas or high performance liquid chromatography with a chiral column. Choice of the appropriate chiral column, eluent and conditions necessary to effect separation of the enantiomeric pair is well within the knowledge of one of ordinary skill in the art.
The terms xe2x80x9cRxe2x80x9d and xe2x80x9cSxe2x80x9d are used herein as commonly used in organic chemistry to denote specific configuration of a chiral center. The term xe2x80x9cRxe2x80x9d (rectus) refers to that configuration of a chiral center with a clockwise relationship of group priorities (highest to second lowest) when viewed along the bond toward the lowest priority group. The term xe2x80x9cSxe2x80x9d (sinister) refers to that configuration of a chiral center with a counterclockwise relationship of group priorities (highest to second lowest) when viewed along the bond toward the lowest priority group. The priority of groups is based upon their atomic number (in order of decreasing atomic number). A partial list of priorities and a discussion of stereochemistry is contained in xe2x80x9cNomenclature of Organic Compounds: Principles and Practicexe2x80x9d, (J. H. Fletcher, et al., eds., 1974) at pages 103-120.
As used herein the term xe2x80x9cLgxe2x80x9d refers to a suitable leaving group. Examples is of suitable leaving groups are Cl, Br, and the like.
The compounds of formula I can be prepared, for example, following analogous procedures set forth in International Patent Application Publication WO 98/33496 published Aug. 6, 1998 (See Example 196 therein). More specifically, the compounds of formula I and formula Ia can be prepared, for example, as disclosed in Scheme I. The reagents and starting materials are readily available to one of ordinary skill in the art. All substituents, unless otherwise specified are as previously defined. 
In Scheme I, step A, the nitrile (1) is hydrogenated to provide the primary amine (2) as the HCl salt. For example, nitrile (1) is dissolved in a suitable organic solvent, such as ethanol, treated with a suitable hydrogenation catalyst, such as palladium on carbon, treated with concentrated HCl and placed under hydrogen at a pressure and temperature sufficient to effect reduction of the nitrile (1) to the primary amine (2). The reaction is then filtered and the filtrate concentrated to provide crude primary amine (2) as the HCl salt. This crude material is then purified by techniques well known in the art, such as recrystallization from a suitable solvent.
In Scheme I, step B, the primary amine (2) HCl salt can be treated with a suitable resolving agent to provide the salt (3). For example, the primary amine (2) HCl salt is dissolved in a suitable organic solvent, such as ethanol and treated with about an equivalent of a suitable base, such as sodium hydroxide. The reaction is filtered and the filtrate is treated with a suitable resolving agent, such as L-malic acid. For example, about 0.25 equivalents of L-malic acid in a suitable organic solvent, such as ethanol is added to the filtrate. The solution is then heated to about 75xc2x0 C. and stirred for about 30 minutes. The solution is then allowed to cool slowly with stirring. The precipitate is then collected by filtration, rinsed with ethanol and dried under vacuum to provide the salt (3). The salt (3) is then suspended in a suitable organic solvent, such as ethanol and water is added. The slurry is heated at reflux until the solids go into solution. The solution is then allowed to cool slowly with stiring for about 8 to 16 hours. The suspension is further cooled to about 0 to 5xc2x0 C. and the salt (3) is collected by filtration. The salt (3) is then rinsed with ethanol and dried at about 35xc2x0 C.
In Scheme I, step C, salt (3) is converted to the free base (4) and in Step D, free base (4) is sulfonylated to provide sulfonamide (5). For example, salt (3) is slurried in a suitable organic solvent, such as methylene chloride and treated with about 2 equivalents of a suitable base, such as aqueous sodium hydroxide. The mixture is stirred for about one hour and the organic phase is separated. The organic phase is then dried, for example by azeotropic distallation with heptane to provide the free base (4). The dried free base (4) in heptane is then treated, for example, with a catalytic amount of 4-dimethylaminopyridine, an excess of triethylamine and methylene chloride is added to provide total dissolution. The solution is cooled to about 5xc2x0 C. and treated with about one equivalent of a compound of formula Lgxe2x80x94SO2CH(CH3)2, such as isopropylsulfonyl chloride. The reaction is then allowed to warm to room temperature over about 16 hours. The reaction is then cooled to about 8xc2x0 C. and treated with 2N aqueous HCl. The organic phase is then separated and washed with water, sodium bicarbonate, dried over anhydrous sodium sulfate, filtered, and concentrated under vacuum to provide sulfonamide (5).
In Scheme I, step E, sulfonamide (5) is nitrated to provide the p-nitro derivative (6). More specifically, sulfonamide (5) is combined with trifluoroacetic acid in a suitable organic solvent mixture, such as methylene chloride and heptane. The mixture is cooled to about xe2x88x925xc2x0 C. and about 1.2 equivalents of 98% fuming nitric acid is added to the mixture. The reaction is then stirred at about xe2x88x925xc2x0 C. to 5xc2x0 C. for about 3 to about 5 hours and then warmed to room temperature. The reaction mixture is then diluted with methylene chloride and water, and mixed for about 15 minutes. The aqueous phase is then separated and extracted with methylene chloride. The organic phase and organic extracts are combined, treated with water and aqueous base, such as 10% sodium hydroxide. The pH is adjusted to about 6.5 to about 7.5 with saturated sodium carbonate. The mixture is stirred for about 10 to 15 minutes and the organic layer is separated. The organic layer is then concentrated under vacuum to provide crude p-nitro derivative (6) which is carried on directly to step F.
In Scheme I, step F, p-nitro derivative (6) is reduced to the p-amino derivative (7) and isolated as a suitable salt, such as a p-toluenesulfonate salt. More specifically, crude p-nitro derivative (6) is dissolved inethanol, treated with a suitable hydrogenation catalyst, such as palladium on carbon and placed under hydrogen at a pressure sufficient to effect reduction of the p-nitro derivative (6) to the p-amino derivative (7). The reaction is filtered, the filtrate concentrated under vacuum, and the crude p-amino derivative (7) is dissolved in a suitable organic solvent, such as tetrahydrofuran. To this solution is added an equivalent of a suitable acid, such as p-toluenesulfonic acid monohydrate with stirring. To this solution is then added MTBE and the slurry is stirred for about 1 to 2 hours. The slurry is then filtered and rinsed with MTBE/THF (3:1) to provide purified p-amino derivative (7).
In Scheme I, step G, the p-amino derivative (7) is converted to the corresponding free base (8). For example, p-amino derivative (7) is suspended in a suitable organic solvent, such as methylene chloride and treated with a suitable base, such as saturated aqueous sodium bicarbonate until the pH of the aqueous phase is about 6.5. The phases are separated, and the organic phase is rinsed with 5% sodium bicarbonate, water, and then concentrated under vacuum to provide free base (8). To this is added diethyl ether, or more preferably, methyl t-butyl ether, to effect crystallization. The resulting solid is collected by filtration to provide purified free base (8).
In Scheme I, step H, free base (8) is treated with a 3,5-dibenzoyl chloride to provide the compound of formula Ia. For example, free base (8) is combined with about 1.15 equivalents triethylamine in a suitable organic solvent, such as methylene chloride. About 1.1 equivalents of 3,5-difluorobenzoyl chloride is added to the solution at room temperature and stirred forabout 1 hour. The reaction mixture is then washed with water and dilute aqueous acid. The organic phase is then diluted with acetone and washed with saturated potassium carbonate, dilute aqueous acid, dried over anhydrous magnesium sulfate, filtered and concentrated under vacuum with addition of ethyl acetate. The residue is crystallized by addition of a suitable organic solvent, such as ethyl acetate. The resulting solids are collected by filtration and dried under vacuum to provide the compound of formula Ia.
In addition, step B can be skipped and the primary amine (2) HCl salt can be carried on directly to step D after converting it to the free base. In this manner the compound of formula I is ultimately prepared.
Alternatively, the compounds of formula Ia can also be prepared, for example, as further disclosed in Scheme II. The reagents and starting materials are readily available to one of ordinary skill in the art. All substituents, unless otherwise specified are as previously defined. 
In Scheme II, step A, the acid (9) can be treated with a suitable resolving agent to provide the salt (10). For example, acid (9) is dissolved in a suitable organic solvent, such as ethyl acetate, the solution is heated to about 30xc2x0 C. and treated with 0.5 equivalents of a suitable resolving agent, such as S-(xe2x88x92)-xcex1-methylbenzylamine. The reaction mixture is then heated at reflux for about 10 minutes and then cooled to room temperature with stirring over about 8 hours to about 16 hours. The resulting precipitate is collected by filtration to provide crude salt (10). The crude salt (10) is reslurried in ethyl acetate at reflux for about 10 minutes and then cooled to room temperature with stirring over about 8 hours to about 16 hours. The salt (10) is collected by filtration, and the above reslurrying process is repeated. The collected salt (10) is then dried under vacuum.
In Scheme II, step B, the salt (10) is treated with aqueous acid under standard conditions well known to one of ordinary skill in the art to provide the free acid (11). For example salt (10) is combined with a suitable organic solvent, such as methylene chloride and treated with 1N HCl. After stirring the reaction mixture for about 1 to about 3 hours, the layers are separated, the organic layer is dried over anhydrous magnesium sulfate, filtered, and concentrated under vacuum to provide free acid (11).
In Scheme II, step C, acid (11) reduced with a suitable reducing agent to provide the primary alcohol (12). For example, acid (11) is dissolved in a suitable organic solvent, such as tetrahydrofuran and treated with a suitable reducing agent, such as borane dimethylsulfide. The reaction is then heated at reflux for about 5 hours, cooled to room temperature and quenched with saturated potassium carbonate. The reaction mixture is then stirred for about 3 hours and the top organic layer is separated. The aqueous layer is extracted with a suitable organic solvent, such as methylene chloride. The organic layer and organic extracts are combined, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered, and concentrated under vacuum to provide the primary alcohol (12).
In Scheme II, step D, primary alcohol (12) is converted to the phthalimide derivative (13). For example, primary alcohol (12) is combined with about one equivalent of phthalimide and about 1.5 equivalents triphenylphosphine in a suitable organic solvent, such as tetrahydrofuran. To this solution is added about 1.5 equivalents of diethyl azodicarboxylate. The reaction mixture is then stirred for about 8 hours to about 16 hours, quenched with water and extracted with a suitable organic solvent, such as methylene chloride. The organic extracts are combined, dried over anhydrous magnesium sulfate, filtered, and concentrated under vacuum. The residue purified by running through a plug of silica gel with a suitable eluent, such as ethyl acetatelhexane (1:1) to provide the phthalimide derivative (13).
In Scheme II, step E, the phthalimide derivative (13) is converted to the primary amine (14). For example, phthalimide derivative (13) is combined with a suitable organic solvent, such as toluene and treated with an excess of hydrazine or a suitable hydrazine equivalent. The reaction mixture is stirred for about 45 minutes, heated at about 90xc2x0 C. to about 95xc2x0 C. until starting material disappears, cooled to about 0xc2x0 C. and the primary amine (14) is collected by filtration.
In Scheme II, step F, the primary amine (14) is sulfonylated to provide sulfonamide (6) in a manner analogous to the procedure described in Scheme I, step D above.
In Scheme II, step G, the sulfonamide (6) is reduced.to provide the free base (8) in a manner analogous to the procedure described in Scheme I, step F above.
In Scheme II, step H, the free base (8) is treated with a 3,5-dibenzoyl chloride to provide the compound of formula Ia in a manner analogous to the procedure described in Scheme 1, step H.
In addition, in Scheme II, step A can be skipped and the acid (9) can be carried on directly to reduction step C. In this manner the compound of formula I is ultimately prepared.
The following examples are illustrative only and are not intended to limit the invention in any way. The reagents and starting materials are readily available to one of ordinary skill in the art. Unless indicated otherwise, the substituents are defined as hereinabove. It is understood by one of ordinary skill in the art that the (R) and (S) enantiomers of formula I can be prepared by starting with, for example, (R)-2-phenyl-1-propylamine or (S)-2-phenyl-1-propylamine, rather than the racemate of 2-phenyl-1-propylamine, or by resolving the compound of formula I using standard techniques well known in the art, such as those described by J. Jacques, et al., xe2x80x9cEnantiomers, Racemates, and Resolutionsxe2x80x9d, John Wiley and Sons, Inc., 1981. Examples of such resolutions include recrystallization techniques or chiral chromatography.
As used herein, the following terms have the meanings indicated: xe2x80x9ceqxe2x80x9d refers to equivalents; xe2x80x9cgxe2x80x9d refers to grams; xe2x80x9cmgxe2x80x9d refers to milligrams; xe2x80x9cngxe2x80x9d refers to nanograms; xe2x80x9cLxe2x80x9d refers to liters; xe2x80x9cmLxe2x80x9d refers to milliliters; xe2x80x9cxcexcLxe2x80x9d refers to microliters;
xe2x80x9cmolxe2x80x9d refers to moles; xe2x80x9cmmolxe2x80x9d refers to millimoles; xe2x80x9cpsixe2x80x9d refers to pounds per square inch; xe2x80x9cminxe2x80x9d refers to minutes; xe2x80x9chxe2x80x9d refers to hours; xe2x80x9cxc2x0 C.xe2x80x9d refers to degrees Celsius; xe2x80x9cTLCxe2x80x9d refers to thin layer chromatography; xe2x80x9cHPLCxe2x80x9d refers to high performance liquid chromatography; xe2x80x9cGCxe2x80x9d refers to gas chromatography; xe2x80x9cRfxe2x80x9d refers to retention factor; xe2x80x9cxcex4xe2x80x9d prefers to part per million down-field from tetramethylsilane; xe2x80x9cTHFxe2x80x9d refers to tetrahydrofuran; xe2x80x9cDMFxe2x80x9d refers to N,N-dimethylformamide; xe2x80x9cDMSOxe2x80x9d refers to methyl sulfoxide; xe2x80x9cLDAxe2x80x9d refers to lithium diisopropylamide; xe2x80x9caqxe2x80x9d refers to aqueous; xe2x80x9ciPrOAcxe2x80x9d refers to isopropyl acetate; xe2x80x9cEtOAcxe2x80x9d refers to ethyl acetate; xe2x80x9cEtOHxe2x80x9d refers to ethyl alcohol; xe2x80x9cMeOHxe2x80x9d refers to methanol; xe2x80x9cMTBExe2x80x9d refers to tert-butyl methyl ether, xe2x80x9cDEADxe2x80x9d refers to diethyl azodicarboxylate; xe2x80x9cTMEDAxe2x80x9d refers to N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, and xe2x80x9cRTxe2x80x9d refers to room temperature.